1. Field of the Invention
The present invention relates to an electrophotographic photoconductor; and an image forming method, an image forming apparatus and a process cartridge each using the electrophotographic photoconductor.
2. Description of the Related Art
In recent years, image forming apparatuses such as copiers, laser printers and facsimiles have increasingly been required to achieve high image quality.
Electrophotographic photoconductors used for image formation are rotated and subjected to necessary or intended treatments such as charging, latent image formation, developing and transferring with various units arranged around them.
For achieving high image quality, it is necessary to perform each treatment uniformly on the entire electrophotographic photoconductor. The electrophotographic photoconductors are rotated during these treatments and thus, are required to have high runout accuracy.
In general, an electrophotographic photoconductor has a metal tube and a photoconductive layer, and flanges are provided at openings of both ends of the metal tube.
The metal tube is produced through extruding, drawing and surface treatment.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2007-025270 discloses a metal tube having a total runout of 80 μm relative to a driving axis thereof.
However, use of such a metal tube having a large total runout cannot accurately superpose multicolor images on top of another (inaccurate superposition of multicolor images), not providing high-quality images. Further, the metal tube is a hollow tube and thus, the larger the outer diameter thereof, the more difficult attainment of high runout accuracy.
Extrusion for producing a metal tube has generally been performed with the porthole method. However, as disclosed in JP-A No. 2002-287395, the metal tube produced with the porthole method has a seam, so that it has a low inner-diameter roundness. Even when this metal tube is subjected to drawing and surface treatments, an electrophotographic photoconductor having a high runout accuracy cannot be obtained.
Also, conventionally, in an attempt to attain high total runout accuracy, the metal tube is cut with its deformation or strain being corrected by holding means (see JP-A Nos. 2008-292882 and 2006-255881). However, even in this case, when released from the holding means after completion of cutting, the metal tube is returned to the original shape; i.e., deformed or strained again, problematically causing a drop in total runout accuracy.
In the recent applications such as full color printing, inaccurate superposition of multicolor images becomes problematic. Especially in image forming apparatuses for the commercial printing market, the number of toners increases from four—black, yellow, magenta and cyan—to five or six—those four colors plus clear color and/or special color, in order to respond to a variety of printing applications. Thus, inaccurate superposition of multicolor images becomes problematic more and more.